This invention relates to railroad switches and particularly to mechanisms for detecting the movements of the switches, or switch points, that function to alter train directions.
It is well known in the railroad arts to provide an electric motor-driven switch machine for positioning a railroad track at a switching point, and coupling therewith a railpoint detection and indication mechanism. In particular, the detection and indication mechanism includes a sensor that identifies a condition when the railroad tracks are not at, or near, their proper positions before or after switching of the railroad tracks.
The traditional approach with a railpoint detection and indication mechanism is to provide a mechanical rod that moves with the switch points. The rod interacts with levers and cams inside of the switch machine or switch circuit controller and the lever is actually a series of dry contacts. These contacts are used for indication by means of vital relays or vital interlocking processor type systems.
A variety of mechanical systems have been proposed or produced over the years but since they usually call for mechanical rods and the like, they require substantial adjustment every so often. They may also involve finger contacts, toggling arms, rotary cam switches, and the like. The large amount of adjustment, sometimes required monthly, is a substantial drawback to such mechanical systems or arrangements for detecting switchpoint movement, and the cost is high because the maintenance is so labor intensive.
Accordingly, it is a primary object of the present invention to eliminate the labor intensive adjustments required with mechanical arrangements and to provide a contactless point detector system that will completely eliminate the need for constant adjustment of parts.
Another object of the present invention is to provide a fast and easy way to adjust switch point detector system involving push button electronic calibration such that the maintainer will simply insert his obstruction gauge in the points and then press a calibration button. Moreover, because of the lack of contacts, mechanical wear is absolutely minimized and the system is inexpensive, when compared to the traditional, dry contact switch and lever approach.
It will be understood that in the operation of the detection system of the present invention, the movement of the switchpoints is produced by a conventional or standard form of switch machine in which an electric motor, or hand throw mechanism, provides the power for the selected movement.
Briefly stated then, the system of the invention is a contactless detection system for detecting the movement of the switchpoints of a railroad switch, such system including a transformer means for detecting or sensing the position of the switchpoints. The transformer means has a ferrous core that is linked to the switch points, and both a primary coil and a pair of secondary coils are wound around the core. The preferred form of this transformer means is referred to as a linear variable differential transformer (LVDT). An electronic interface means is further included for receiving signals from the secondary coils of the transformer responsive to, and corresponding with, the positioning of the switch points.
The system of the invention will also detect the position of the stock rail. Occasionally, the stock rail moves with respect to the railroad ties due to the track hardware loosening up. As the stock rail moves, the switch points move. The LVDT senses this movement and indicates that the stock rail has shifted.
An additional major feature of the present invention resides in the provision of operational vitality by which is meant that the detector or sensor is arranged to be vital such that any failure must cause the system to be as safe as the system was before the failure. The linear variable differential transformer forming an essential part of the system can fail in many different modes including 1) shorts in one or more coils to ground; 2) shorts from the primary coil to one or more secondary coils; 3) shorts from secondary to secondary; 4) one or more of the coils failing open; 5) change in resistance in one or more of the coils (up or down); 6) damaged core.
The foregoing and still further objects and advantages of the present invention will be more apparent from the following detailed explanation of the preferred embodiments of the invention in connection with the accompanying drawings: